There has been a remarkable development in electronic projection image technology in recent years and, with the arrival of the electronic information age, the electronic still camera has become popular. However, electronic still cameras are somewhat expensive for their performance as compared with a photographic camera that uses silver chloride film, and this has been an obstacle to the electronic still camera being even more popular. Because of this, the development of an inexpensive zoom lens that is suited for an electronic still camera is particularly desired.
There have been several examples of prior art zoom lenses suitable for use in electronic still cameras, video cameras, and the like. For example, in Japan Laid-Open Patent Publication H07-113956, there is disclosed a zoom lens having, in order from the object side, a negative first lens group and positive second lens group. This wide-angle zoom lens requires at least seven lens elements. In addition, in Japan Laid-Open Patent Publication H09-179026 there is disclosed a four-group zoom lens, with the groups having negative, positive, negative, and positive power, respectively, in order from the object side. This zoom lens also requires at least 7 lens elements.
These prior art zoom lenses are neither necessarily compact nor inexpensive. In zoom lenses used in electronic still cameras and the like, wide-angle zoom lenses are required which have a short focal distance with respect to the size of the image plane, a small number of lens elements so as to be compact, and the zoom lens must yield a high-quality image. However, at the wide-angle end, because the lens outer diameter becomes large when the size of the image picture plane is made large, there is a possibility of losing compactness as a result of enlargement of the lens barrel diameter.
Although not a zoom lens, a wide-angle lens having two focal points is disclosed in Japan Laid-Open Patent Publication H06-201993. This lens has at least seven elements in three lens groups, with the lens groups being arranged, in order from the object side, as follows: a negative first lens group, a positive second lens group, and a positive third lens group. However, this wide-angle lens cannot be said to be compact due to its comparatively large front lens group diameter.